Bash – The simple but correct way to have a bash script send output to systemd journal

bashlogsshell-scriptsystemdsystemd-journald

I have simply been sticking something like this at the top of my bash scripts. This still works with systemd. (I have used it for a long time and I don't fully understand it. It just works, so I use it.)

exec 5> >(logger -t $0)
BASH_XTRACEFD="5"
PS4='$LINENO: '
set -x

Even with systemd, the above commands give the expected output in journalctl. However, it seems that maybe I should be using something like this instead.

systemd-cat -t $0

How should I alter my current logging commands under systemd?

(I'm looking for the same kind of simple-minded solution where I can paste a few lines and get some output in the journal.)

Best Answer

I would stick with logger: it works with any standards-compliant logging system, including systemd’s journal as you’ve discovered. Using systemd-cat directly would only make your scripts systemd-specific, without adding anything; in fact, modern logger is much more flexible, and provides better support for systemd-specific features than systemd-cat itself.

Related Solutions

Fedora – How to get access to the root journal for systemd

The systemd-journald man page explains how journal access control is done:

Journal files are, by default, owned and readable by the "systemd-journal"
system group but are not writable. Adding a user to this group thus enables
her/him to read the journal files.

By default, each logged in user will get her/his own set of journal files in
/var/log/journal/. These files will not be owned by the user, however, in order
to avoid that the user can write to them directly. Instead, file system ACLs
are used to ensure the user gets read access only.

Additional users and groups may be granted access to journal files via file
system access control lists (ACL).

Fedora 20 uses ACLs to give users in the adm and wheel groups read access to all the journals.

how to give a normal user also access to the root journal?

Run setfacl -n -m u:username:r /var/log/journal/*/system.journal .

how to get list which journals are available for a given user?

You can su to the user and run journalctl --header|grep '^File Path' to see the names of the journals he or she has access to.

getfacl can be used to see which groups and users have access to journal files. I don't know of a simple way to list the files that are readable by a specific user.

Bash – script can’t write to systemd journal

Use systemd-cat. It connects a pipeline or program output with the journal.

Example:

printf "Write text to the journal" | systemd-cat

Result:

journalctl -xn
[..]
Apr 12 13:37:00 servername [31509]: Write text to the journal

If you want to identify the logging tool you can add the -t option:

printf "Write text to the journal" | systemd-cat -t yourIdentifier
journalctl -xn
Apr 12 13:37:00 servername yourIdentifier[31833]: Write text to the journal

Edit: To show messages for the specified syslog identifier only, use the -t option:

journalctl -t yourIdentifier

This parameter can be specified multiple times.

Best Answer

Related Solutions

Fedora – How to get access to the root journal for systemd

Bash – script can’t write to systemd journal

Related Question